FIG. 1 shows a conventional fuel injector having a traditional three-part design of an inner metal flow guidance part and housing component at the same time. This inner valve tube is formed by an inlet connection piece forming an internal pole, a nonmagnetic intermediate part and a valve seat carrier holding the valve seat, as explained in greater detail in the description of FIG. 1.
German Published Patent Application No. 35 02 287 describes a method for manufacturing a hollow cylindrical metal housing having two magnetizable housing parts including a nonmagnetic housing zone between them, forming a magnetic isolation between the housing parts. This metal housing is premachined in one piece from a magnetizable blank down to an excess outside diameter, a ring groove being cut in the inside wall of the housing in the width of the desired middle housing zone. In the case of a rotating housing, a nonmagnetizable filler material is filled into the ring groove, while the ring groove area is heated up, and rotation of the housing is continued until the filling material solidifies. The housing is then turned on the outside down to the final dimension of the outside diameter, so that there is no longer a connection between the magnetizable housing parts. A valve housing manufactured in this way may be used, e.g., in solenoid valves for antilock brake systems (ABS) in motor vehicles.
In addition, methods for manufacturing a solid core for fuel injectors for internal combustion engines are described in German Published Patent Application No. 42 37 405 (FIG. 5 of the document). These methods are characterized in that a one-piece sleeve-shaped magnetic martensitic workpiece which is provided directly or via prior transformation processes undergoes a local heat treatment in a middle section of the magnetic martensitic workpiece to convert this middle section into a nonmagnetic, austenitic middle section. Elements forming austenite and/or ferrite molten by laser during the local heat treatment are alternatively added at the site of the heat treatment to form a nonmagnetic, austenitic middle section of the solid core.